Staphylococcus aureus is a Gram-positive pathogenic bacterium affecting man and his domestic animals; it lends itself well to routine genetic analysis and laboratory manipulation. At the present time it is one of a limited number of pathogenic bacteria which are being studied at the genetic level. It is thus not only an important pathogen in its own right, but serves as a model in the genetic characterization of gram-positive pathogens. The primary goal of the proposed research is to characterize this bacterium in terms of the genetic organization of the chromosome, and to recognize those attributes which are associated with pathogenicity which are determined by extrachromosomal genetic determinants. Presently, we have "mapped" 13 genetic markers (1 pigment, two antibiotic-resistance, and 10 auxotrophic) into three linkage groups by genetic transformation. The upper limit of linkages demonstrable by transformation is greater (about 3-fold) than by transduction. Additional markers are being sought to extend this analysis towards the eventual definition of the chromosome as (a single ?) a linkage group. Within this map it should be possible to determine the genetic location of genetic determinants of virulence and pathogenicity, phage-typing patterns, etc. BIBLIOGRAPHIC REFERENCES: Lye, D. J., and P. A. Pattee. 1975. Some requirements for the development of competence in Staphylococcus aureus. Abstracts of the Annual Meeting of the American Soc. Microbiol. 1975:H41 (ABSTRACT). Pattee, P.A., and D.A. Neveln. 1975. Three major linkage groups in Staphylococcus aureus demonstrated by transformation. Abstracts of the Annual Meeting of the American Soc. Microbiol. 1975:H42 (ABSTRACT).